In patients with asthma mucous cells appear in airways that are normally devoid of these cells. This phenotype is called mucous cell metaplasia (MCM). MCM poses a serious risk because acutely secreted mucus can reduce airflow or can sometimes completely obstruct the airways and lead to death of asthmatics. In addition, epidemiological studies suggest that patients with chronic MCM are at a higher risk of developing lung cancer. Our studies demonstrated that IFN? and STAT1 signaling are crucial for the resolution of MCM by inducing cell death in airway epithelial cells (AECs). Therefore, this renewal application is focused on delineating the molecular mechanisms by which IFN? induces cell death in AECs. IFN? activates ERK1/2 and translocates Bax to the endoplasmic reticulum (ER) and reduces MCM. We found that Bik, a Bcl-2 family member that localizes to the ER, was significantly reduced in AECs obtained by bronchial brushings from asthmatics compared to controls. AECs from bik-/- mice were unaffected by IFN?, and Bik overexpression caused activation of ERK1/2 and induced killing in AECs. Noxa, another Bcl-2 family member, is induced by IFN? and enhances Bik-induced apoptosis. Noxa interacts with phosphorylated HSP27, reduces I?B levels, co-localizes with NF-?B, and reduces Bcl-2 mRNA expression. These findings led us to the following hypothesis: IFN?-induced cell death is mediated by Bik-induced activation of ERK1/2 that results in the translocation of Bax to the ER to initiate apoptosis. Furthermore, the Bik-mediated apoptosis is enhanced by Noxa through its interaction with phopho-HSP27 to degrade I?B1 but inhibit nuclear translocation of activated NF-?B and decrease Bcl-2 expression. We will test this hypothesis by: (1) Investigating whether Bik is central for the IFN?-induced cell death and resolution of MCM by activating ERK1/2 and translocating Bax to the ER. (2) Determining whether Noxa cross-linked to phosphorylated HSP27 facilitates NF-?B activation but inhibits nuclear translocation of NF-?B and thereby decreases Bcl-2 mRNA expression to enhance Bik-induced cell death and to identify the domain of Noxa-HSP27 interaction. (3) Determining whether Bik-induced ER stress requires Bax and Bak for the resolution of MCM during prolonged exposure to allergen. Understanding the role of these proteins in the resolution process of MCM may allow us to reduce hyperplastic epithelial cells that can secrete excessive mucus in asthmatics without compromising the resting epithelial cells and therefore the barrier functions of the epithelium. Development of targeted approaches to reduce MCM may also be useful for eliminating pre-neoplastic cells in patients with an increased risk of developing lung cancer.

Public Health Relevance

. Increased number of mucous cells in the airways poses a serious risk because acutely secreted mucus can reduce airflow or can sometimes completely obstruct the airways and lead to death of asthmatics. The proposed studies will dissect the molecular sequence of events that underlies the normal resolution process for these mucous cells during prolonged exposure to allergen in normal mice. Understanding these molecular processes may provide new strategies for reducing mucous secretions by eliminating hyperplastic mucous cells.